Aluminum distearate composition and greases prepared therefrom



ALUMINUM DISTEARATE COMPOSITION AND GREASES PREPARED THEREFROM NoDrawing. Application November 28, 1951, Serial No. 258,747

3 Claims. (Cl. 252-35) This invention relates to aluminum soaps andgrease compositions containing the same. More particularly, it relatesto new and improved aluminum salts of higher fatty acids, which areknown in the trade as grease grade aluminum stearates, and to greasecompositions of im proved gel strength prepared therewith Greasescomposed of hydrocarbon oils thickened with aluminum soaps are wellknown. The aluminum salts of higher fatty acids used for this purposeare known in the trade as aluminum stearates, even though the fattyacids from which they are prepared are not all stearic acid. Thus, forexample, hydrogenated fish oil fatty acids having the followingcompositions are used:

Hydrogenated tallow acids and other similar higher fatty acid mixturesare also used in the manufacture of grease grade aluminum stearates, andaluminum soaps thereof are included within the scope of the presentinvention.

Aluminum stearate is manufactured commercially by reacting a watersolution of the sodium soap of a commercial fatty acid with a solutionof an aluminum salt, generally the sulfate. The resulting slurry ofinsoluble aluminum stearate is filtered, washed, dried, and ground touniform particle size.

In general, stearates with aluminum to fatty acid ratios correspondingto the distearate have proved most effective in the preparation oflubricating greases. Ordinarily, these aluminum soaps are added tohydrocarbon mineral oils in the ratio of about 4% to 12% or more of thesoap to 96% to 88% hydrocarbon oil, respectively. Hydrocarbonlubricating oils having Saybolt 'viscosities within the range of 100-120seconds at 210 F. are frequently used. The grease is compounded byheating the mixture of oil and aluminum soap until maximum dispersion ofthe soap in the oil is obtained. The grease is then cooled undercontrolled conditions during which the optimum gel structure is built upin the grease.

We have found that the gel-forming power of aluminum distearate, asdefined above, in hydrocarbon oils, can be greatly improved by formingaluminum distearate anhydride therein. Our present invention isdirected, therefore, to aluminum distearate anhydride, to grease gradealuminum distearate containingsubstantial quantities (i. e., 1% byweight or more) of aluminum distearate anhydride therein, and to methodsfor the production of these improved products.

The aluminum distearate anhydrides of this invention are characterizedby the substantial absence of chemically combined water and are not tobe confused with the dehydrated soaps of the prior art in which onlyphysically present water has been removed.

The formation of our new compounds is shown by the following equation:

O O 120 110 CR O O 0 2 AI-OH Al-O-Al H20 0 O 0 R0; R0; ;CR 0 O O atent2,702,792 Patented Feb. 22, 1955 0 OH O Al Al-OH O RC O OH AlO-Al +H2O OO RC; 012

wherein R is the same.

The aluminum distearate anhydrides, as defined above, are prepared bythe dehydration of the corresponding aluminum distearates. Thisdehydration, we have found, can be effected by heating the previouslydried aluminum distearate with agitation at temperatures of 160-180" C.or higher for a length of time suflicient to remove all of thechemically combined water, and thus to produce the anhydride. Thealuminum distearate anhydrides so obtained are white solids that aresoluble or dispersible in aliphatic hydrocarbons such as kerosene,lubricating oils and the like.

We have also found, however, as another important feature of ourinvention, that an increase in the gelforming power of aluminumdistearates is obtainable by only partial conversion thereof to aluminumdistearate anhydride. The advantage of this discovery is, of course,that considerably less drastic heating conditions are required to effectthe partial dehydration. Thus, for example, we have found thatsubstantial quantities of aluminum distearate anhydride, ranging from 1%to about 15-25%, can be formed by heating aluminum distearate underdehydrating conditions for a suitable time, usually within about 1-5hours, at a temperature of at least 160 0, when stagnant heatingconditions are used. We have also found, however, that the same degreeof dehydration can be effected at much lower temperatures, which may beas low as C., if the aluminum distearate is heated in a current ofdrying gas such as hot air or hot products of combustion.

Any suitable type of equipment may be used to carry out the process ofour invention. Where stagnant heating is employed, i. e., where thealuminum distearate is simply heated with agitation to drive out water,an indirect-fired kiln or a jacketed kettle provided with internalagitation may be used. When a current of hot air or other drying gas isemployed, we prefer to use a belt dryer or a tray dryer in which acurrent of the drying gas is passed continuously over the aluminumdistearate in finely divided form. Other similar equipment will readilysuggest itself to those experienced in the art of drying solids, and maybe employed.

The invention will be further illustrated by the following specificexamples, which describe specific embodiments thereof, but to which itis not limited.

Example 1 An aluminum soap was prepared from hydrogenated fish oil fattyacids by the method previously described; i. e., by adding aluminumsulfate solution to a water solution of the sodium soap of the acids at70 C., washing the resulting precipitate free from sodium sulfate, anddrying in a current of hot air on a belt dryer. The dried soap contained1.0% moisture and 8.74% A: and was composed essentially of aluminumdistearate.

Samples of this soap were heated for 90 minutes in open containerssuspended in oil baths at varying temperatures. Where necessary, theheated material was ground and screened to 40 mesh. Greases containingof the soaps were then made in a hydrocarbon lubricating oil having aviscosity of 300 at 100 F. and tested with the penetrometer both inunworked condition and after working for 60 strokes. The test resultsare shown in the following table, in which penetrations are in tenths ofa millimeter.

These results show clearly the increase in gel strength that follows theformation of increasing amounts of aluminum distearate anhydride in thealuminum soap composition as progressively higher heating temperaturesare used. Tests made by heating samples of the same soap at 160 C. forincreasing times show a much slower increase in gel strength; thus, forexample, a grease prepared with the same quantity of the samehydrocarbon oil, but using a soap heated at 160 C. for 2 /2 hours showeda penetration of 152 unworked and 250 worked. It is evident, therefore,that the anhydride is not formed by the stagnant heating of aluminumdistearate soaps at temperatures much below 160 C. At temperatures above160 C., however, the anhydride formation is quite rapid Example 2 Wehave also found that aluminum distearate anhydride can be formed attemperatures considerably below 160 C. when a stream of hot drying gasesis employed. Hot air or hot combustion products of hydrocarbon oil ornatural gas may be used for this purpose.

Samples of the washed precipitate of Example 1 were extruded intostrings which were caught on perforated trays. These were placed in anoven arranged to blow hot air downwardly through the stearate and weredried and dehydrated under the conditions shown in the table below. Thesamples were then made into 10% dispcrsions in the hydrocarbon oil ofExample 1 and greases were made and tested as described in that exampleand alsolafter working for 1000 strokes with the following resu ts:

These figures show that substantial quantities of the anhydride,sufficient to increase materially the gel strength of greases andbelieved to range from about 5% to 25% of the weight of the soap, areobtainable when aluminum distearate is dried in a current of hot gasesat temperatures of -135 C. Comparison of the penetrations with those ofExample 1 will show that the results are comparable with those obtainedby heating the soap in a stagnant atmosphere at C. for 1 /2 hours.

From the foregoing it will be seen that the present invention, inefiect, substitutes a new type of grease grade aluminum stearate forthose previously employed, with a resulting increase in the gel strengthof the grease. It will be evident that a smaller proportion of the newaluminum stearate may be employed, as compared with the quantities ofordinary aluminum stearates, when an increase in gel strength is not ofimportance. It will also be evident that the new aluminum distearateanhydride may be used in admixture with ordinary aluminum distearate orother metallic soaps if desired. It will be understood, therefore, thata variety of grease compositions may be prepared by those skilled in theart within the scope of the appended claims.

What I claim is:

1. Aluminum distearate anhydride.

2. A grease grade aluminum distearate of improved gel-forming power inhydrocarbon oils, said aluminum distearate having a substantial contentof aluminum distearate anhydride therein.

3. A grease composition comprising a major proportion of a hydrocarbonlubricating oil and a minor quantity within the range of about 4% to 12%by weight of an aluminum distearate having a substantial content ofaluminum distearate anhydride therein.

References Cited in the file of this patent UNITED STATES PATENTS2,211,139 Licata Aug. 13, 1940 2,297,183 Fabian et al Sept. 29, 19422,359,946 Sudholz et al. Oct. 10, 1944 2,447,064 Gebhart et al. Aug. 17,1948 2,555,104 Ashley et al. May 29, 1951 OTHER REFERENCES MetallicSoaps, Raw Materials for Research and Incllislstlr yl pub. Metasap Chem.Co., 1940, pages 3, 4 and

3. A GREASE COMPOSITION COMPRISING A MAJOR PROPORTION OF A HYDROCARBONLUBRICATING OIL AND A MINOR QUANTITY WITHIN THE RANGE OF ABOUT 4% TO 12%BY WEIGHT OF AN ALUMINUM DISTEARATE HAVING A SUBSTANTIAL CONTENT OFALUMINUM DISTEARATE ANHYDRIDE THEREIN.